As described in U.S. Pat. No. 5,787,566 of Stursberg standard machining apparatus has a frame and a conveyor on the frame extending in a normally horizontal workpiece travel direction and adapted to support a flat workpiece. A tool mount displaceable on the frame transversely of the direction carries at least one a material-removing tool, e.g. a drill or a miller, for machining the workpiece with generation of particles. A drive roller engageable with an upper surface of the workpiece upstream of the tool advances the workpiece in the direction past the tools.
Such a machine can do programmed work. Typically the drive roller, which is in solid contact with the workpiece, is connected to a position detector that feeds to a central controller exact information about the exact position of the workpiece relative to the tools, which are then operated by the controller to do their various machining jobs at the appropriate locations.
Since such machining must often be carried out even very close to the downstream end of the workpiece it is necessary to position the drive unit including the drive roller very close to the machining station having the tools. This creates the problem of getting particles produced by the machining operation into the workpiece drive. Such particles are hard so that they can damage the drive roller and mar the workpiece finish. Furthermore they can allow the drive roller to slip on the workpiece which will cause the workpiece to be ruined.